Figures

- Relationship of Vibrio Species Infection and Elevated Temperatures to Yellow Blotch/Band Disease in Caribbean Corals

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FIG. 1. (A and B) Classic blotching yellow bands developing on the tissue of Montastraea spp. as described previously (8, 56). (C and D) Classic healthy Montastraea sp. during June 1997 and images of the same colony 5 months later with yellow lesions affecting half of the colony. This coral remains alive, with 50% of it overgrown with algae.

FIG. 3. (a) Corals exposed to higher temperatures over time expel more of their symbiotic zooxanthellae from the gastroderm. (b) Corals exposed to bacterial pathogens coupled with increasing temperatures experience zooxanthella degradation within the gastroderm.

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FIG. 4. Lesion advancement after inoculation with YB pathogens together with increasing temperatures. The bar graph represents the area of YBD on experimental corals. At various times and temperatures, the zones of infection were estimated and the areas were calculated, and these values were plotted versus time. The error bars indicate standard deviations.

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FIG. 5. (a) Histology of Montastraea sp. exposed to YBD pathogens at 20°C. Vacuolation and slight fragmentation are evident. However, host structural features are also evident, indicating early breakdown. e, epidermis; m, mesogleoa; g, gastroderm; v, vacuole. Magnification, x7,440. (b) Histological section of Montastraea sp. exposed to 25°C for 72 h. Symbiotic zooxanthella degeneration and vacuolation are extreme. The host tissue structural morphology has changed due to the virulence of YBD bacteria coupled with higher temperature. The mesogleoa is no longer evident. Magnification, x7,440. zoox, symbiotic algae. (c) Light microscopic image of healthy zooxanthellae 8 h after inoculation with Vibrio. Evidence of algal lysis is seen surrounding the bacterial mat. Magnification, x 400. (d) Healthy zooxanthella isolated from controls. The average diameter of a cell in control tissues is 1.14 cm at a print magnification of x1,250. This means that the unit diameter of the zooxanthella is 0.01 mm. Magnification, x 1,000.

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FIG. 6. Transmission electron micrographs (TEMs) of symbiotic zooxanthellae exposed to 25°C with symptoms of YBD. Degradation of the cell wall appears to be evident, along with vacuolation and cytoplasmic shrinkage. TEMs of zooxanthellae in situ indicate the same general morphology seen in light microscopy but reveal far greater detail. The chloroplasts are displaced to the outer margin of the cell; however, they appear intact. There are numerous non-membrane-bound vacuoles that appear within the nucleus and cytoplasm of the zooxanthellae. Some of these are filled with an electron-dense substance, but many are empty or filled with fluid. The cores of the algal cells are severely vacuolated. The normal morphology of the algal cell is disturbed beyond recognition, and the surface configuration of many organelles is unrecognizable. The pyrenoid body is apparent and normal in structure. However, in some cells, especially after being heated to 32°C, the pyrenoid is fragmented into separate segments. Algal swelling in the 32°C samples is primarily attributable to the expansion of the accumulation bodies and separation of the algal surface membranes from the peripheral cytoplasm containing chloroplasts. n, nucleus; CL, chloroplasts; S, starch vacuoles; cw, cell wall. Scale bars, 0.2 µm.